1 /* vi: set sw=4 ts=4: */
4 * Bjorn Wesen, Axis Communications AB (bjornw@axis.com)
6 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
8 * ---------------------------------------------------------------------------
9 * (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN
10 ****************************************************************************
12 * The telnetd manpage says it all:
14 * Telnetd operates by allocating a pseudo-terminal device (see pty(4)) for
15 * a client, then creating a login process which has the slave side of the
16 * pseudo-terminal as stdin, stdout, and stderr. Telnetd manipulates the
17 * master side of the pseudo-terminal, implementing the telnet protocol and
18 * passing characters between the remote client and the login process.
20 * Vladimir Oleynik <dzo@simtreas.ru> 2001
21 * Set process group corrections, initial busybox port
33 #include <arpa/telnet.h>
35 /* Structure that describes a session */
37 struct tsession *next;
38 int sockfd_read, sockfd_write, ptyfd;
41 /* two circular buffers */
42 /*char *buf1, *buf2;*/
43 /*#define TS_BUF1 ts->buf1*/
44 /*#define TS_BUF2 TS_BUF2*/
45 #define TS_BUF1 ((unsigned char*)(ts + 1))
46 #define TS_BUF2 (((unsigned char*)(ts + 1)) + BUFSIZE)
47 int rdidx1, wridx1, size1;
48 int rdidx2, wridx2, size2;
51 /* Two buffers are directly after tsession in malloced memory.
52 * Make whole thing fit in 4k */
53 enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 };
58 static struct tsession *sessions;
60 static const char *loginpath = "/bin/login";
62 static const char *loginpath = DEFAULT_SHELL;
64 static const char *issuefile = "/etc/issue.net";
68 Remove all IAC's from buf1 (received IACs are ignored and must be removed
69 so as to not be interpreted by the terminal). Make an uninterrupted
70 string of characters fit for the terminal. Do this by packing
71 all characters meant for the terminal sequentially towards the end of buf.
73 Return a pointer to the beginning of the characters meant for the terminal.
74 and make *num_totty the number of characters that should be sent to
77 Note - If an IAC (3 byte quantity) starts before (bf + len) but extends
78 past (bf + len) then that IAC will be left unprocessed and *processed
79 will be less than len.
81 FIXME - if we mean to send 0xFF to the terminal then it will be escaped,
82 what is the escape character? We aren't handling that situation here.
84 CR-LF ->'s CR mapping is also done here, for convenience.
86 NB: may fail to remove iacs which wrap around buffer!
88 static unsigned char *
89 remove_iacs(struct tsession *ts, int *pnum_totty)
91 unsigned char *ptr0 = TS_BUF1 + ts->wridx1;
92 unsigned char *ptr = ptr0;
93 unsigned char *totty = ptr;
94 unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
103 /* We now map \r\n ==> \r for pragmatic reasons.
104 * Many client implementations send \r\n when
105 * the user hits the CarriageReturn key.
107 if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
111 * TELOPT_NAWS support!
113 if ((ptr+2) >= end) {
114 /* only the beginning of the IAC is in the
115 buffer we were asked to process, we can't
116 process this char. */
121 * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
123 else if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
127 break; /* incomplete, can't process */
128 ws.ws_col = (ptr[3] << 8) | ptr[4];
129 ws.ws_row = (ptr[5] << 8) | ptr[6];
130 ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
133 /* skip 3-byte IAC non-SB cmd */
135 fprintf(stderr, "Ignoring IAC %s,%s\n",
136 TELCMD(ptr[1]), TELOPT(ptr[2]));
143 num_totty = totty - ptr0;
144 *pnum_totty = num_totty;
145 /* the difference between ptr and totty is number of iacs
146 we removed from the stream. Adjust buf1 accordingly. */
147 if ((ptr - totty) == 0) /* 99.999% of cases */
149 ts->wridx1 += ptr - totty;
150 ts->size1 -= ptr - totty;
151 /* move chars meant for the terminal towards the end of the buffer */
152 return memmove(ptr - num_totty, ptr0, num_totty);
156 static struct tsession *
158 USE_FEATURE_TELNETD_STANDALONE(int sock)
159 SKIP_FEATURE_TELNETD_STANDALONE(void)
161 const char *login_argv[2];
162 struct termios termbuf;
165 struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);
167 /*ts->buf1 = (char *)(ts + 1);*/
168 /*ts->buf2 = ts->buf1 + BUFSIZE;*/
170 /* Got a new connection, set up a tty. */
171 fd = getpty(tty_name, 32);
173 bb_error_msg("can't create pty");
180 #if ENABLE_FEATURE_TELNETD_STANDALONE
181 ts->sockfd_read = sock;
183 if (!sock) { /* We are called with fd 0 - we are in inetd mode */
184 sock++; /* so use fd 1 for output */
187 ts->sockfd_write = sock;
191 /* ts->sockfd_read = 0; - done by xzalloc */
192 ts->sockfd_write = 1;
196 /* Make the telnet client understand we will echo characters so it
197 * should not do it locally. We don't tell the client to run linemode,
198 * because we want to handle line editing and tab completion and other
199 * stuff that requires char-by-char support. */
201 static const char iacs_to_send[] ALIGN1 = {
202 IAC, DO, TELOPT_ECHO,
203 IAC, DO, TELOPT_NAWS,
204 IAC, DO, TELOPT_LFLOW,
205 IAC, WILL, TELOPT_ECHO,
206 IAC, WILL, TELOPT_SGA
208 memcpy(TS_BUF2, iacs_to_send, sizeof(iacs_to_send));
209 ts->rdidx2 = sizeof(iacs_to_send);
210 ts->size2 = sizeof(iacs_to_send);
213 fflush(NULL); /* flush all streams */
214 pid = vfork(); /* NOMMU-friendly */
218 /* sock will be closed by caller */
219 bb_perror_msg("vfork");
229 /* Careful - we are after vfork! */
231 /* make new session and process group */
234 /* Restore default signal handling */
235 bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
237 /* open the child's side of the tty. */
238 /* NB: setsid() disconnects from any previous ctty's. Therefore
239 * we must open child's side of the tty AFTER setsid! */
240 fd = xopen(tty_name, O_RDWR); /* becomes our ctty */
244 while (fd > 2) close(fd--);
245 tcsetpgrp(0, getpid()); /* switch this tty's process group to us */
247 /* The pseudo-terminal allocated to the client is configured to operate in
248 * cooked mode, and with XTABS CRMOD enabled (see tty(4)). */
249 tcgetattr(0, &termbuf);
250 termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
251 termbuf.c_oflag |= ONLCR | XTABS;
252 termbuf.c_iflag |= ICRNL;
253 termbuf.c_iflag &= ~IXOFF;
254 /*termbuf.c_lflag &= ~ICANON;*/
255 tcsetattr(0, TCSANOW, &termbuf);
257 /* Uses FILE-based I/O to stdout, but does fflush(stdout),
258 * so should be safe with vfork.
259 * I fear, though, that some users will have ridiculously big
260 * issue files, and they may block writing to fd 1,
261 * (parent is supposed to read it, but parent waits
262 * for vforked child to exec!) */
263 print_login_issue(issuefile, NULL);
265 /* Exec shell / login / whatever */
266 login_argv[0] = loginpath;
267 login_argv[1] = NULL;
268 /* exec busybox applet (if PREFER_APPLETS=y), if that fails,
269 * exec external program */
270 BB_EXECVP(loginpath, (char **)login_argv);
271 /* _exit is safer with vfork, and we shouldn't send message
272 * to remote clients anyway */
273 _exit(1); /*bb_perror_msg_and_die("execv %s", loginpath);*/
276 /* Must match getopt32 string */
278 OPT_WATCHCHILD = (1 << 2), /* -K */
279 OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
280 OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p */
281 OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
284 #if ENABLE_FEATURE_TELNETD_STANDALONE
287 free_session(struct tsession *ts)
289 struct tsession *t = sessions;
291 if (option_mask32 & OPT_INETD)
294 /* Unlink this telnet session from the session list */
298 while (t->next != ts)
304 /* It was said that "normal" telnetd just closes ptyfd,
305 * doesn't send SIGKILL. When we close ptyfd,
306 * kernel sends SIGHUP to processes having slave side opened. */
307 kill(ts->shell_pid, SIGKILL);
308 wait4(ts->shell_pid, NULL, 0, NULL);
311 close(ts->sockfd_read);
312 /* We do not need to close(ts->sockfd_write), it's the same
313 * as sockfd_read unless we are in inetd mode. But in inetd mode
314 * we do not reach this */
317 /* Scan all sessions and find new maxfd */
321 if (maxfd < ts->ptyfd)
323 if (maxfd < ts->sockfd_read)
324 maxfd = ts->sockfd_read;
326 /* Again, sockfd_write == sockfd_read here */
327 if (maxfd < ts->sockfd_write)
328 maxfd = ts->sockfd_write;
334 #else /* !FEATURE_TELNETD_STANDALONE */
336 /* Used in main() only, thus "return 0" actually is exit(0). */
337 #define free_session(ts) return 0
341 static void handle_sigchld(int sig)
346 /* Looping: more than one child may have exited */
348 pid = wait_any_nohang(NULL);
353 if (ts->shell_pid == pid) {
362 int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
363 int telnetd_main(int argc, char **argv)
365 fd_set rdfdset, wrfdset;
369 #if ENABLE_FEATURE_TELNETD_STANDALONE
370 #define IS_INETD (opt & OPT_INETD)
371 int master_fd = master_fd; /* be happy, gcc */
372 unsigned portnbr = 23;
373 char *opt_bindaddr = NULL;
382 /* Even if !STANDALONE, we accept (and ignore) -i, thus people
383 * don't need to guess whether it's ok to pass -i to us */
384 opt = getopt32(argv, "f:l:Ki" USE_FEATURE_TELNETD_STANDALONE("p:b:F"),
385 &issuefile, &loginpath
386 USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr));
387 if (!IS_INETD /*&& !re_execed*/) {
388 /* inform that we start in standalone mode?
389 * May be useful when people forget to give -i */
390 /*bb_error_msg("listening for connections");*/
391 if (!(opt & OPT_FOREGROUND)) {
392 /* DAEMON_CHDIR_ROOT was giving inconsistent
393 * behavior with/without -F, -i */
394 bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv);
397 /* Redirect log to syslog early, if needed */
398 if (IS_INETD || !(opt & OPT_FOREGROUND)) {
399 openlog(applet_name, 0, LOG_USER);
400 logmode = LOGMODE_SYSLOG;
402 USE_FEATURE_TELNETD_STANDALONE(
404 portnbr = xatou16(opt_portnbr);
407 /* Used to check access(loginpath, X_OK) here. Pointless.
408 * exec will do this for us for free later. */
410 #if ENABLE_FEATURE_TELNETD_STANDALONE
412 sessions = make_new_session(0);
413 if (!sessions) /* pty opening or vfork problem, exit */
414 return 1; /* make_new_session prints error message */
416 master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
417 xlisten(master_fd, 1);
420 sessions = make_new_session();
421 if (!sessions) /* pty opening or vfork problem, exit */
422 return 1; /* make_new_session prints error message */
425 /* We don't want to die if just one session is broken */
426 signal(SIGPIPE, SIG_IGN);
428 if (opt & OPT_WATCHCHILD)
429 signal(SIGCHLD, handle_sigchld);
430 else /* prevent dead children from becoming zombies */
431 signal(SIGCHLD, SIG_IGN);
434 This is how the buffers are used. The arrows indicate the movement
436 +-------+ wridx1++ +------+ rdidx1++ +----------+
437 | | <-------------- | buf1 | <-------------- | |
438 | | size1-- +------+ size1++ | |
440 | | rdidx2++ +------+ wridx2++ | |
441 | | --------------> | buf2 | --------------> | |
442 +-------+ size2++ +------+ size2-- +----------+
444 size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
445 size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"
447 Each session has got two buffers. Buffers are circular. If sizeN == 0,
448 buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
455 /* Select on the master socket, all telnet sockets and their
456 * ptys if there is room in their session buffers.
457 * NB: scalability problem: we recalculate entire bitmap
458 * before each select. Can be a problem with 500+ connections. */
461 struct tsession *next = ts->next; /* in case we free ts. */
462 if (ts->shell_pid == -1) {
463 /* Child died and we detected that */
466 if (ts->size1 > 0) /* can write to pty */
467 FD_SET(ts->ptyfd, &wrfdset);
468 if (ts->size1 < BUFSIZE) /* can read from socket */
469 FD_SET(ts->sockfd_read, &rdfdset);
470 if (ts->size2 > 0) /* can write to socket */
471 FD_SET(ts->sockfd_write, &wrfdset);
472 if (ts->size2 < BUFSIZE) /* can read from pty */
473 FD_SET(ts->ptyfd, &rdfdset);
478 FD_SET(master_fd, &rdfdset);
479 /* This is needed because free_session() does not
480 * take master_fd into account when it finds new
481 * maxfd among remaining fd's */
482 if (master_fd > maxfd)
486 count = select(maxfd + 1, &rdfdset, &wrfdset, NULL, NULL);
488 goto again; /* EINTR or ENOMEM */
490 #if ENABLE_FEATURE_TELNETD_STANDALONE
491 /* First check for and accept new sessions. */
492 if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
494 struct tsession *new_ts;
496 fd = accept(master_fd, NULL, NULL);
499 /* Create a new session and link it into our active list */
500 new_ts = make_new_session(fd);
502 new_ts->next = sessions;
510 /* Then check for data tunneling. */
512 while (ts) { /* For all sessions... */
513 struct tsession *next = ts->next; /* in case we free ts. */
515 if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
518 /* Write to pty from buffer 1. */
519 ptr = remove_iacs(ts, &num_totty);
520 count = safe_write(ts->ptyfd, ptr, num_totty);
528 if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
532 if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
533 /* Write to socket from buffer 2. */
534 count = MIN(BUFSIZE - ts->wridx2, ts->size2);
535 count = safe_write(ts->sockfd_write, TS_BUF2 + ts->wridx2, count);
543 if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
547 /* Should not be needed, but... remove_iacs is actually buggy
548 * (it cannot process iacs which wrap around buffer's end)!
549 * Since properly fixing it requires writing bigger code,
550 * we rely instead on this code making it virtually impossible
551 * to have wrapped iac (people don't type at 2k/second).
552 * It also allows for bigger reads in common case. */
553 if (ts->size1 == 0) {
557 if (ts->size2 == 0) {
562 if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
563 /* Read from socket to buffer 1. */
564 count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
565 count = safe_read(ts->sockfd_read, TS_BUF1 + ts->rdidx1, count);
567 if (count < 0 && errno == EAGAIN)
571 /* Ignore trailing NUL if it is there */
572 if (!TS_BUF1[ts->rdidx1 + count - 1]) {
577 if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */
581 if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
582 /* Read from pty to buffer 2. */
583 count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
584 count = safe_read(ts->ptyfd, TS_BUF2 + ts->rdidx2, count);
586 if (count < 0 && errno == EAGAIN)
592 if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */